This application is based on and claims priority to Japanese Patent Application No. 10-323257, filed Nov. 13, 1998, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention relates to oil injection lubrication for engines, and more particularly to an oil injection system and methods for lubricating a multiple cylinder two-cycle engine.
2. Description of the Related Art
For two-cycle engines, it is a common practice to mix lubricating oil with induction air to lubricate engine parts. Conventional systems typically mix oil with induction air in the same proportion regardless of engine speed. Under certain conditions, however, some cylinders of some engines require more lubricating oil than other cylinders. In multiple cylinder engines the temperature of the cylinders may differ from one another possibly due to differences in the cooling system capacity. These variations in temperature necessitate variations in the amount of lubricating oil delivered to the different cylinders. Typical oil injection systems deliver the same amount of oil to each cylinder regardless of the engine operating conditions. Operating conditions such as cylinder resting periods, idling periods, rapid acceleration periods, or continuous speed periods, however, often result in variations in the appropriate amount of oil required for each cylinder. In addition, variations in the lengths of exhaust runners for each cylinder of a two-cycle engine cause variations in the volumetric flow through each cylinder.
Typical outboard marine engines also have a vertically disposed crankshaft, which causes lubricating oil to descend from the upper cylinders to the lower cylinders. This orientation further exacerbates the differential in lubrication needs between the cylinders.
Conventional systems do not provide the capability of adjusting the amount of oil delivered to each cylinder to compensate for these situations. Consequently, conventional systems suffer from problems such as smoke generated by the mixture of air and lube oil, odor, and heavy oil consumption.
Existing systems for single cylinder engines provide a solenoid valve at a discharge side of a mechanical oil pump through which oil delivery can be regulated in response to varying engine operating conditions. In these systems, however, the oil pump is typically configured to supply oil at a constant volume per crankshaft revolution. At extremely low engine speeds, an engine may require much less oil per revolution than at higher speeds. As a consequence, the solenoid valves may have to be actuated in a relatively heavy duty cycle to appropriately regulate the flow of oil at low engine speeds. Actuation of the solenoid valves draws electrical power. Consequently these systems adversely draw a relatively large amount of electrical power during low engine speed periods when it is also more difficult to generate electrical power. Still another disadvantage of existing systems is that they would require a complicated layout of solenoid valves and lines in order to be adapted to multiple cylinder engines.
The present invention provides an improved oil injection lubrication system and associated methods for an engine, which has particular application in connection with a multi-cylinder engine.
In accordance with one aspect of the present invention, the system comprises a variable output oil pump, the output of which can be varied in relation to a throttle valve position. A solenoid valve unit, which includes a plurality of solenoid valves, regulates the flow of oil from the oil pump to each cylinder. An electronic control unit sends control signals to the solenoid valve unit to regulate the flow of oil based upon engine operating conditions in accordance with a control scheme. By adjusting the output from the oil pump in accordance with the throttle position, the volume of oil directed to each cylinder is roughly equal (i.e., approximates) to a predetermined volume of oil required or desired for a given engine speed or operational condition. The solenoid valve unit then regulates the volume flow to each cylinder through the solenoid valves to fine tune the amount of oil delivered to each cylinder (including both the combustion chamber and the corresponding crankcase section) to more precisely equal the predetermined volume, that volume depending upon the engine""s running condition.
In a preferred mode, one solenoid valve is dedicated to each cylinder. The valve circuitry is configured to permit oil flow from the oil pump to the cylinders when the corresponding solenoid valves are in an inactive state. An electronic control unit (ECU) powers the solenoid valves to temporarily close the valves and direct a portion of the lubricant flow away from the cylinders (e.g., through a line to an oil tank). By varying the closure times of the valves, the ECU can finely tune the amount of oil delivered to each cylinder in accordance with predetermined control strategies.
In accordance with this aspect of the present invention, a lubrication system is provided for an engine having a plurality of cylinders. The system comprises a plurality of oil supply pipes, each oil supply pipe being configured to supply oil to one of the plurality of cylinders. A solenoid valve unit is connected to the plurality of oil supply pipes and regulates the flow of oil to the cylinders. An oil pump is connected to the solenoid valve unit to supply oil to the unit, and an electronic control unit is connected to and communicates with the solenoid valve unit to control the operation of the unit.
In one mode, an oil supply pipe carries a flow of oil from the valve unit to a vapor separator tank for mixture with the fuel supply in order to reduce the formation of deposits on fuel injectors, lubricate the fuel system, and/or prevent corrosion.
A preferred method of controlling oil delivery to the cylinders of an engine comprises producing a base volume flow of oil per crankshaft revolution. The base volume is adjusted per crankshaft revolution to deliver an adjusted volume per crankshaft revolution. This adjusted volume is then fine tuned for each cylinder.
In a preferred mode of operation, the base volume per crankshaft revolution is supplied through a positive displacement oil pump, and the base volume per crankshaft revolution is adjusted by varying the volume output per revolution by the positive displacement oil pump. The volume supplied per revolution by the positive displacement oil pump is preferably adjusted in relation to a position of a throttle valve of the engine. The adjusted volume is then fine tuned by passing the adjusted volume through a solenoid valve. The ECU preferably fine tunes the adjusted volume based on a number of factors relating to the operation of the engine. The factors may include those that apply to all of the engine""s cylinders (i.e., do not differ between the cylinders), such as intake air temperature, atmospheric pressure, battery voltage, engine break-in period, and load frequency among others. The factors may also include those that differ between the cylinders, such as cylinder resting periods, different combustion efficiency due to exhaust runner length differences, different cylinder cooling capacities, and oil leak down from upper cylinders to lower cylinders, among other factors.
In one mode, the ECU determines a fine tuning of a first cylinder based upon at least one factor that applies to all of the cylinders. The ECU then determines the fine tuning of the additional cylinders based upon at least one factor that differs between the cylinders. The ECU preferably uses a compensation control map to adjust the oil supply for each of the remaining cylinders.
Further aspects, features and advantages of the present invention will become apparent from the detailed description of the preferred embodiment which follows.